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Abstract:

A vehicle drive device includes an input coupled to an internal
combustion engine; an output coupled to wheels; first and second rotary
electric machines; a differential including at least three rotary
elements; a control; and an engagement device. The control determines,
when engine stop conditions are established while the engagement device
is drivably connected, the engine is operating, and the output member is
rotating, whether rotation of the first electric machine when stop
conditions are established is opposite to rotation of the first electric
machine when rotation of the engine stops; executes torque control where
the first electric machine outputs torque to reduce the rotational speed
of the engine when the stop establishing rotational direction is opposite
to the subject rotational direction; and issues a command to release the
drivable connection when the rotational speed of the first electric
machine falls within a rotational speed range that includes zero.

Claims:

1. A vehicle drive device comprising: an input member drivably coupled to
an internal combustion engine; an output member drivably coupled to
wheels; a first rotary electric machine; a second rotary electric
machine; a differential gear device including at least three rotary
elements; a control device; and an engagement device, wherein the input
member, the output member, and the first rotary electric machine are
drivably coupled to different rotary elements of the differential gear
device via no other rotary element of the differential gear device, the
second rotary electric machine is drivably coupled to one of the rotary
elements of the differential gear device other than the rotary element to
which the first rotary electric machine is drivably coupled, via no other
rotary element of the differential gear device, the engagement device is
capable of releasing drivable connection between one of the input member,
the output member, and the first rotary electric machine and the
corresponding rotary element of the differential gear device, and the
control device includes a rotational direction determination section
that, when internal combustion engine stop conditions for stopping the
internal combustion engine are established in a state in which the
drivable connection made by the engagement device is maintained, the
internal combustion engine is in operation, and the output member is
rotating, determines whether or not a stop condition establishing
rotational direction, which is a rotational direction of the first rotary
electric machine at the time when the internal combustion engine stop
conditions are established, is opposite to a subject rotational
direction, which is a rotational direction of the first rotary electric
machine at an operation point at which a rotational speed of the internal
combustion engine becomes zero, a rotation reducing torque control
section that executes rotation reducing torque control in which the first
rotary electric machine is caused to output rotation reducing torque in a
direction to reduce the rotational speed of the internal combustion
engine on condition that it is determined that the stop condition
establishing rotational direction is opposite to the subject rotational
direction, and a connection release command section that issues a command
to release the drivable connection made by the engagement device on
condition that the rotational speed of the first rotary electric machine
falls within a connection release rotational speed range set so as to
include zero.

2. The vehicle drive device according to claim 1, wherein the connection
release command section issues the command to release the drivable
connection made by the engagement device before the rotational direction
of the first rotary electric machine becomes the same as the subject
rotational direction.

3. The vehicle drive device according to claim 2, wherein the rotation
reducing torque control section stops the rotation reducing torque
control before the rotational direction of the first rotary electric
machine becomes the same as the subject rotational direction.

4. The vehicle drive device according to claim 3, wherein the control
device executes fluctuation suppressing control in which the second
rotary electric machine is caused to output fluctuation suppressing
torque for suppressing torque fluctuations to be transferred to the
output member via the differential gear device because of variations in
state of operation of the first rotary electric machine or variations in
state of engagement of the engagement device.

5. The vehicle drive device according to claim 4, wherein the second
rotary electric machine is drivably coupled to the rotary element of the
differential gear device to which the output member is drivably coupled,
via no other rotary element of the differential gear device.

6. The vehicle drive device according to claim 5, wherein the
differential gear device includes three rotary elements that are a first
rotary element, a second rotary element, and a third rotary element in
the order of rotational speed, the first rotary electric machine is
drivably coupled to the first rotary element, the input member is
drivably coupled to the second rotary element, and the second rotary
electric machine and the output member are drivably coupled to the third
rotary element, via no other rotary element of the differential gear
device, and the engagement device is provided on a power transfer path
between the input member and the second rotary element.

7. The vehicle drive device according to claim 1, wherein the second
rotary electric machine is drivably coupled to one of the rotary elements
of the differential gear device other than the rotary element to which
the first rotary electric machine is drivably coupled or the rotary
element to which the output member is drivably coupled, via no other
rotary element of the differential gear device, and the engagement device
is provided on a power transfer path between the input member and the
rotary element of the differential gear device to which the input member
is drivably coupled via no other rotary element.

8. The vehicle drive device according to claim 1, wherein the control
device executes fluctuation suppressing control in which the second
rotary electric machine is caused to output fluctuation suppressing
torque for suppressing torque fluctuations to be transferred to the
output member via the differential gear device because of variations in
state of operation of the first rotary electric machine or variations in
state of engagement of the engagement device.

9. The vehicle drive device according to claim 1, wherein the second
rotary electric machine is drivably coupled to the rotary element of the
differential gear device to which the output member is drivably coupled,
via no other rotary element of the differential gear device.

10. The vehicle drive device according to claim 1, wherein the
differential gear device includes three rotary elements that are a first
rotary element, a second rotary element, and a third rotary element in
the order of rotational speed, the first rotary electric machine is
drivably coupled to the first rotary element, the input member is
drivably coupled to the second rotary element, and the second rotary
electric machine and the output member are drivably coupled to the third
rotary element, via no other rotary element of the differential gear
device, and the engagement device is provided on a power transfer path
between the input member and the second rotary element.

11. The vehicle drive device according to claim 2, wherein the control
device executes fluctuation suppressing control in which the second
rotary electric machine is caused to output fluctuation suppressing
torque for suppressing torque fluctuations to be transferred to the
output member via the differential gear device because of variations in
state of operation of the first rotary electric machine or variations in
state of engagement of the engagement device.

12. The vehicle drive device according to claim 2, wherein the second
rotary electric machine is drivably coupled to the rotary element of the
differential gear device to which the output member is drivably coupled,
via no other rotary element of the differential gear device.

13. The vehicle drive device according to claim 2, wherein the
differential gear device includes three rotary elements that are a first
rotary element, a second rotary element, and a third rotary element in
the order of rotational speed, the first rotary electric machine is
drivably coupled to the first rotary element, the input member is
drivably coupled to the second rotary element, and the second rotary
electric machine and the output member are drivably coupled to the third
rotary element, via no other rotary element of the differential gear
device, and the engagement device is provided on a power transfer path
between the input member and the second rotary element.

14. The vehicle drive device according to claim 2, wherein the second
rotary electric machine is drivably coupled to one of the rotary elements
of the differential gear device other than the rotary element to which
the first rotary electric machine is drivably coupled or the rotary
element to which the output member is drivably coupled, via no other
rotary element of the differential gear device, and the engagement device
is provided on a power transfer path between the input member and the
rotary element of the differential gear device to which the input member
is drivably coupled via no other rotary element.

15. The vehicle drive device according to claim 3, wherein the second
rotary electric machine is drivably coupled to the rotary element of the
differential gear device to which the output member is drivably coupled,
via no other rotary element of the differential gear device.

16. The vehicle drive device according to claim 3, wherein the
differential gear device includes three rotary elements that are a first
rotary element, a second rotary element, and a third rotary element in
the order of rotational speed, the first rotary electric machine is
drivably coupled to the first rotary element, the input member is
drivably coupled to the second rotary element, and the second rotary
electric machine and the output member are drivably coupled to the third
rotary element, via no other rotary element of the differential gear
device, and the engagement device is provided on a power transfer path
between the input member and the second rotary element.

17. The vehicle drive device according to claim 3, wherein the second
rotary electric machine is drivably coupled to one of the rotary elements
of the differential gear device other than the rotary element to which
the first rotary electric machine is drivably coupled or the rotary
element to which the output member is drivably coupled, via no other
rotary element of the differential gear device, and the engagement device
is provided on a power transfer path between the input member and the
rotary element of the differential gear device to which the input member
is drivably coupled via no other rotary element.

18. The vehicle drive device according to claim 8, wherein the second
rotary electric machine is drivably coupled to the rotary element of the
differential gear device to which the output member is drivably coupled,
via no other rotary element of the differential gear device.

19. The vehicle drive device according to claim 18, wherein the
differential gear device includes three rotary elements that are a first
rotary element, a second rotary element, and a third rotary element in
the order of rotational speed, the first rotary electric machine is
drivably coupled to the first rotary element, the input member is
drivably coupled to the second rotary element, and the second rotary
electric machine and the output member are drivably coupled to the third
rotary element, via no other rotary element of the differential gear
device, and the engagement device is provided on a power transfer path
between the input member and the second rotary element.

20. The vehicle drive device according to claim 8, wherein the second
rotary electric machine is drivably coupled to one of the rotary elements
of the differential gear device other than the rotary element to which
the first rotary electric machine is drivably coupled or the rotary
element to which the output member is drivably coupled, via no other
rotary element of the differential gear device, and the engagement device
is provided on a power transfer path between the input member and the
rotary element of the differential gear device to which the input member
is drivably coupled via no other rotary element.

Description:

INCORPORATION BY REFERENCE

[0001] The disclosure of Japanese Patent Application No. 2011-094322 filed
on Apr. 20, 2011 including the specification, drawings and abstract is
incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a vehicle drive device including
an input member drivably coupled to an internal combustion engine, an
output member drivably coupled to wheels, a first rotary electric
machine, a second rotary electric machine, a differential gear device
including at least three rotary elements, and a control device.

DESCRIPTION OF THE RELATED ART

[0003] An example of the vehicle drive device described above according to
the related art is described in Japanese Patent Application Publication
No. 2010-76678 (JP 2010-76678 A) (paragraph 0049 etc.). JP 2010-76678 A
describes a device in which a differential gear device is formed by a
planetary gear mechanism including three rotary elements, namely a sun
gear to which a first rotary electric machine is drivably coupled, a
carrier to which an input member is drivably coupled, and a ring gear to
which a second rotary electric machine and an output member are drivably
coupled. Such a configuration makes it possible to establish a hybrid
travel mode, in which the vehicle is run utilizing torque of the internal
combustion engine, and an electric travel mode, in which the vehicle is
run using torque of the second rotary electric machine with the internal
combustion engine stopped. The vehicle drive device further includes an
engagement device capable of releasing drivable connection between the
carrier and the input member (internal combustion engine). The engagement
device is controlled to a state in which drivable connection between the
carrier and the input member is secured (hereinafter referred to as
"coupled state") during execution of the hybrid travel mode, and to a
state in which drivable connection between the carrier and the input
member is released (hereinafter referred to as "decoupled state") during
execution of the electric travel mode. This allows the internal
combustion engine to be disconnected from the planetary gear mechanism
during execution of the electric travel mode, which enables positively
controlling the rotational speed of the first rotary electric machine to
rotate the carrier and to drive an accessory utilizing rotation of the
carrier as described in JP 2010-76678 A, for example.

[0004] In a configuration in which the engagement device is brought into
the decoupled state during execution of the electric travel mode, as in
the configuration according to JP 2010-76678 A, it is necessary to stop
the internal combustion engine and to switch the engagement device from
the coupled state to the decoupled state when switching is made from the
hybrid travel mode to the electric travel mode as described in paragraph
0049 of Japanese JP 2010-76678 A. In this event, in the configuration
according to JP 2010-76678 A, the engagement device is automatically
switched into the decoupled state by stopping fuel injection of the
internal combustion engine. JP 2010-76678 A also describes switching the
engagement device to the decoupled state by controlling a hydraulic
pressure.

[0005] However, JP 2010-76678 A does not specifically describe the timing
to switch the engagement device from the coupled state to the decoupled
state. Therefore, there has not been revealed a configuration in which
the engagement device can be switched from the coupled state to the
decoupled state at a timing that is suitable from the viewpoint of energy
efficiency, which is important for the vehicle drive device described
above.

SUMMARY OF THE INVENTION

[0006] In view of the foregoing, it is desirable to provide a vehicle
drive device capable of switching an engagement device from a coupled
state to a decoupled state at a timing that is suitable from the
viewpoint of energy efficiency.

[0007] An aspect of the present invention provides a vehicle drive device
including an input member drivably coupled to an internal combustion
engine, an output member drivably coupled to wheels, a first rotary
electric machine, a second rotary electric machine, a differential gear
device including at least three rotary elements, a control device, and an
engagement device. The input member, the output member, and the first
rotary electric machine are drivably coupled to different rotary elements
of the differential gear device via no other rotary element of the
differential gear device. The second rotary electric machine is drivably
coupled to one of the rotary elements of the differential gear device
other than the rotary element to which the first rotary electric machine
is drivably coupled via no other rotary element of the differential gear
device. The engagement device is capable of releasing drivable connection
between one of the input member, the output member, and the first rotary
electric machine and the corresponding rotary element of the differential
gear device. The control device includes: a rotational direction
determination section that, when internal combustion engine stop
conditions for stopping the internal combustion engine are established in
a state in which the drivable connection made by the engagement device is
maintained, the internal combustion engine is in operation, and the
output member is rotating, determines whether or not a stop condition
establishing rotational direction, which is a rotational direction of the
first rotary electric machine at the time when the internal combustion
engine stop conditions are established, is opposite to a subject
rotational direction, which is a rotational direction of the first rotary
electric machine at an operation point at which a rotational speed of the
internal combustion engine becomes zero; a rotation reducing torque
control section that executes rotation reducing torque control in which
the first rotary electric machine is caused to output rotation reducing
torque in a direction to reduce the rotational speed of the internal
combustion engine on condition that it is determined that the stop
condition establishing rotational direction is opposite to the subject
rotational direction; and a connection release command section that
issues a command to release the drivable connection made by the
engagement device on condition that the rotational speed of the first
rotary electric machine falls within a connection release rotational
speed range set so as to include zero.

[0008] The terms "drivably coupled" and "drivable connection" as used
herein refer to a state in which two rotary elements are coupled to each
other in such a way that enables transfer of a drive force, which
includes a state in which the two rotary elements are coupled to each
other to rotate together with each other, and a state in which the two
rotary elements are coupled to each other via one or two or more
transmission members in such a way that enables transfer of a drive
force. Examples of such transmission members include various members that
transfer rotation at an equal speed or a changed speed, such as a shaft,
a gear mechanism, a belt, and a chain. Additional examples of such
transmission members include engagement elements that selectively
transfer rotation and a drive force, such as a friction engagement
element and a meshing-type engagement element. The term "drive force" is
used as a synonym for "torque".

[0009] Herein, a differential gear mechanism including three rotary
elements such as a planetary gear mechanism including a sun gear, a
carrier, and a ring gear is used, and the differential gear mechanism
alone, or a device obtained by combining a plurality of differential gear
mechanisms with each other, is referred to as a differential gear device.

[0010] The term "rotary electric machine" as used herein refers to any of
a motor (electric motor), a generator (electric generator), and a motor
generator that functions both as a motor and as a generator as necessary.

[0011] According to the aspect described above, the direction of torque
(rotation reducing torque) output from the first rotary electric machine
during execution of the rotation reducing torque control coincides with
the direction to reduce the rotational speed of the internal combustion
engine. Immediately after the internal combustion engine is stopped (at
least one of fuel injection and ignition is stopped) upon establishment
of the internal combustion engine stop conditions, a rotation output
member of the internal combustion engine is subjected to inertial torque
matching the moment of inertia of the internal combustion engine in the
direction to continuously rotate. Therefore, the rotation reducing torque
is defined as torque with a predetermined magnitude that resists against
the inertial torque. The rotation reducing torque control is executed on
condition that it is determined that the stop condition establishing
rotational direction is opposite to the subject rotational direction.
Therefore, the direction of the rotation reducing torque at the start of
execution of the rotation reducing torque control coincides with the
direction to reduce the absolute value of the rotational speed of the
first rotary electric machine (direction to generate electricity). Hence,
executing the rotation reducing torque control allows the first rotary
electric machine to regenerate (generate) electric power matching the
magnitude of the inertial torque of the internal combustion engine by
effectively utilizing the inertial torque.

[0012] The first rotary electric machine regenerates electric power
utilizing the inertial torque of the internal combustion engine with the
engagement device in the coupled state. Therefore, it seems to be
preferable that the engagement device should be maintained in the coupled
state during a period until the inertial torque becomes zero. When the
rotational direction of the first rotary electric machine becomes the
same as the subject rotational direction, however, the direction of the
rotation reducing torque becomes the direction to increase the absolute
value of the rotational speed of the first rotary electric machine, and
therefore electric power may not be regenerated utilizing the inertial
torque of the internal combustion engine. In the aspect of the present
invention, in view of this fact, the command to release the drivable
connection made by the engagement device is issued to switch the
engagement device from the coupled state to the decoupled state on
condition that the rotational speed of the first rotary electric machine
falls within the connection release rotational speed range set so as to
include zero. This makes it possible to improve the energy efficiency by
generating electricity by effectively utilizing the inertial torque of
the internal combustion engine, and to suppress energy loss due to
unnecessary rotation of the first rotary electric machine.

[0013] The connection release command section may issue the command to
release the drivable connection made by the engagement device before the
rotational direction of the first rotary electric machine becomes the
same as the subject rotational direction.

[0014] According to this configuration, it is possible to suppress energy
loss caused by the first rotary electric machine rotating unnecessarily
while the first rotary electric machine is not able to generate
electricity, which enhances the energy efficiency.

[0015] The rotation reducing torque control section may stop the rotation
reducing torque control before the rotational direction of the first
rotary electric machine becomes the same as the subject rotational
direction.

[0016] According to this configuration, it is possible to suppress power
running with the first rotary electric machine outputting torque
(rotation reducing torque) that resists against the inertial torque of
the internal combustion engine in a rotational speed range in which
electric power may not be regenerated utilizing the inertial torque,
which further enhances the energy efficiency.

[0017] The control device may execute fluctuation suppressing control in
which the second rotary electric machine is caused to output fluctuation
suppressing torque for suppressing torque fluctuations to be transferred
to the output member via the differential gear device because of
variations in state of operation of the first rotary electric machine or
variations in state of engagement of the engagement device.

[0018] According to this configuration, it is possible to suppress torque
fluctuations to be transferred to the output member drivably coupled to
the wheels. Hence, it is possible to suppress shock to the vehicle when
control for stopping the internal combustion engine is executed upon
establishment of the internal combustion engine stop conditions.

[0019] The second rotary electric machine may be drivably coupled to the
rotary element of the differential gear device to which the output member
is drivably coupled via no other rotary element of the differential gear
device.

[0020] According to this configuration, it is possible to establish an
electric travel mode in which torque of the second rotary electric
machine is transferred to the output member to drive the wheels with the
internal combustion engine stopped irrespective of which of the input
member, the output member, and the first rotary electric machine is the
member for which the engagement device is capable of releasing drivable
connection with the corresponding rotary element of the differential gear
device. Hence, it is possible to enhance the degree of freedom in
designing the arrangement of the engagement device, which makes the
vehicle drive device according to the aspect of the present invention
widely applicable.

[0021] In a configuration in which the engagement device is capable of
releasing the drivable connection between the input member and the
corresponding rotary element of the differential gear device, for
example, the differential gear device may include three rotary elements
that are a first rotary element, a second rotary element, and a third
rotary element in the order of rotational speed; the first rotary
electric machine may be drivably coupled to the first rotary element, the
input member may be drivably coupled to the second rotary element, and
the second rotary electric machine and the output member may be drivably
coupled to the third rotary element, via no other rotary element of the
differential gear device; and the engagement device may be provided on a
power transfer path between the input member and the second rotary
element.

[0022] The term "order of rotational speed" may refer to either of an
order from the high speed side to the low speed side and an order from
the low speed side to the high speed side depending on the rotating state
of each differential gear mechanism. In either case, the order of the
rotary elements is invariable.

[0023] Alternatively, the second rotary electric machine may be drivably
coupled to one of the rotary elements of the differential gear device
other than the rotary element to which the first rotary electric machine
is drivably coupled or the rotary element to which the output member is
drivably coupled via no other rotary element of the differential gear
device; and the engagement device may be provided on a power transfer
path between the input member and the rotary element of the differential
gear device to which the input member is drivably coupled via no other
rotary element.

[0024] Also according to this configuration, it is possible to establish
the electric travel mode in which torque of the second rotary electric
machine is transferred to the output member to drive the wheels with the
internal combustion engine stopped.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 is a skeleton diagram showing the mechanical configuration
of a vehicle drive device according to a first embodiment of the present
invention;

[0026] FIG. 2 is a schematic diagram showing the system configuration of
the vehicle drive device according to the first embodiment of the present
invention;

[0027] FIG. 3 is a velocity diagram illustrating operation of internal
combustion engine stop control according to the first embodiment of the
present invention;

[0028] FIG. 4 is a time chart showing an example of a state of operation
of various components during execution of the internal combustion engine
stop control according to the first embodiment of the present invention;

[0029] FIG. 5 is a flowchart showing the process procedures of the
internal combustion engine stop control according to the first embodiment
of the present invention;

[0030] FIG. 6 is a skeleton diagram showing the mechanical configuration
of a vehicle drive device according to a second embodiment of the present
invention;

[0031] FIG. 7 is a velocity diagram illustrating operation of internal
combustion engine stop control according to the second embodiment of the
present invention;

[0032] FIG. 8 is a skeleton diagram showing the mechanical configuration
of a vehicle drive device according to a third embodiment of the present
invention;

[0033] FIG. 9 is a velocity diagram illustrating operation of internal
combustion engine stop control according to the third embodiment of the
present invention;

[0034] FIG. 10 is a velocity diagram illustrating operation of internal
combustion engine stop control according to a fourth embodiment of the
present invention;

[0035] FIG. 11 is a velocity diagram illustrating operation of internal
combustion engine stop control according to another embodiment of the
present invention;

[0036] FIG. 12 is a velocity diagram illustrating operation of internal
combustion engine stop control according to another embodiment of the
present invention;

[0037] FIG. 13 is a velocity diagram illustrating operation of internal
combustion engine stop control according to another embodiment of the
present invention;

[0038] FIG. 14 is a velocity diagram illustrating operation of internal
combustion engine stop control according to another embodiment of the
present invention; and

[0039] FIG. 15 is a velocity diagram illustrating operation of internal
combustion engine stop control according to another embodiment of the
present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

1. First Embodiment

[0040] A vehicle drive device according to a first embodiment of the
present invention will be described with reference to the drawings. As
shown in FIG. 1, a vehicle drive device 1 according to the embodiment is
a drive device (hybrid vehicle drive device) that drives a vehicle
(hybrid vehicle) including both an internal combustion engine E and
rotary electric machines MG1 and MG2 each serving as a drive force source
for wheels. The vehicle drive device 1 according to the embodiment also
includes a control device 70 (see FIG. 2). The control device 70 controls
operation of the drive force sources and a friction engagement device CL
on the basis of the system configuration shown in FIG. 2. In FIG. 2,
broken lines each indicate a transfer path for electric power, and solid
arrows each indicate a transfer path for various types of information.

[0041] In the embodiment, as shown in FIG. 1, a differential gear device
DG provided in the vehicle drive device 1 is formed by a planetary gear
mechanism PG including a sun gear s, a carrier ca, and a ring gear r each
serving as a rotary element. The first rotary electric machine MG1 is
drivably coupled to the sun gear s, an input member I is drivably coupled
to the carrier ca, and the second rotary electric machine MG2 and an
output member O are drivably coupled to the ring gear r, via no other
rotary element of the planetary gear mechanism PG. The input member I is
drivably coupled to the internal combustion engine E. The output member O
is drivably coupled to wheels W.

[0042] The vehicle drive device 1 further includes the friction engagement
device CL capable of releasing the drivable connection between the input
member I and the carrier ca. This allows the internal combustion engine E
to be disconnected during execution of an electric travel mode (EV travel
mode) in which output torque of the second rotary electric machine MG2 is
transferred to the output member O to drive the wheels W with the
internal combustion engine E stopped. This makes it possible to improve
the energy efficiency by avoiding idling (dragging) of the first rotary
electric machine MG1, to drive an accessory (such as an oil pump)
utilizing rotation of the carrier ca, and so forth. The configuration of
the vehicle drive device 1 according to the embodiment will be described
in detail below.

[0043] 1-1. Mechanical Configuration of Vehicle Drive Device

[0044] First, the mechanical configuration of the vehicle drive device 1
according to the embodiment will be described. The vehicle drive device 1
includes the input member I drivably coupled to the internal combustion
engine E, the output member O drivably coupled to the wheels W, the first
rotary electric machine MG1, the second rotary electric machine MG2, the
differential gear device DG including at least three rotary elements, and
the control device 70. The vehicle drive device 1 according to the
embodiment is formed as a drive device for a hybrid vehicle of a
so-called 2-motor split type including the differential gear device DG
for power distribution which distributes output torque of the internal
combustion engine E to the side of the first rotary electric machine MG1
and the side of the wheels W and the second rotary electric machine MG2.

[0045] In the embodiment, as shown in FIG. 1, the differential gear device
DG is formed by the planetary gear mechanism PG of a single pinion type.
That is, in the example, the differential gear device DG includes three
rotary elements. The three rotary elements of the differential gear
device DG are defined as a first rotary element e1, a second rotary
element e2, and a third rotary element e3 in the order of rotational
speed. Then, in the embodiment, the first rotary element e1 is formed by
the sun gear s of the planetary gear mechanism PG, the second rotary
element e2 is formed by the carrier ca of the planetary gear mechanism
PG, and the third rotary element e3 is formed by the ring gear r of the
planetary gear mechanism PG.

[0046] As discussed later, the input member I, the output member O, and
the first rotary electric machine MG1 are drivably coupled to different
rotary elements of the differential gear device DG via no other rotary
element of the differential gear device DG. The second rotary electric
machine MG2 is drivably coupled to one of the rotary elements of the
differential gear device DG other than the rotary element to which the
first rotary electric machine MG1 is drivably coupled, via no other
rotary element of the differential gear device DG. The vehicle drive
device 1 further includes the friction engagement device CL capable of
releasing the drivable connection between one of the input member I, the
output member O, and the first rotary electric machine MG1 and the
corresponding rotary element of the differential gear device DG.

[0047] A rotary element coupling member is coupled to each of the rotary
elements of the differential gear device DG to rotate together with that
rotary element. Specifically, as shown in FIG. 1, a first rotary element
coupling member 41 is coupled to the sun gear s serving as the first
rotary element e1, a second rotary element coupling member 42 is coupled
to the carrier ca serving as the second rotary element e2, and a third
rotary element coupling member 43 is coupled to the ring gear r serving
as the third rotary element e3. Each of the input member I, the output
member O, the first rotary electric machine MG1, and the second rotary
electric machine MG2 is drivably coupled to any of the rotary element
coupling members to be drivably coupled to any of the rotary elements of
the differential gear device DG.

[0048] The input member I is drivably coupled to the internal combustion
engine E. In the embodiment, the input member I is formed by a shaft
member (input shaft). The internal combustion engine E is a motor that
outputs power through combustion of fuel. Examples of the internal
combustion engine E include spark-ignition engines such as a gasoline
engine and compression-ignition engines such as a diesel engine. The
input member I is drivably coupled to an internal combustion engine
output shaft such as a crankshaft of the internal combustion engine E. In
the embodiment, the input member I is drivably coupled to the internal
combustion engine output shaft to rotate together with the internal
combustion engine output shaft so that the rotational speed of the input
member I is equal to the rotational speed of the internal combustion
engine E. It is also suitable that the internal combustion engine E is
drivably coupled to the input member I via other devices such as a damper
and a flywheel.

[0049] The output member O is drivably coupled to the wheels W. In the
embodiment, the output member O is formed by a gear member, specifically
a differential input gear provided in an output differential gear device
D. In the example, the output differential gear device D is formed by a
differential gear mechanism that uses a plurality of bevel gears that
mesh with each other, and distributes torque transferred to the output
member O to the left and right wheels W serving as drive wheels. The
wheels W are provided with a brake device 93 (in the example, a disc
brake) that applies a braking force matching the amount of operation of a
brake pedal 91 (see FIG. 2) to the wheels W.

[0050] The first rotary electric machine MG1 includes a first stator St1
fixed to a case (not shown) and a first rotor Ro1 supported on the
radially inner side of the first stator St1 so as to be freely rotatable.
The second rotary electric machine MG2 includes a second stator St2 fixed
to the case (not shown) and a second rotor Ro2 supported on the radially
inner side of the second stator St2 so as to be freely rotatable. The
second rotor Ro2 is drivably coupled to a second rotary electric machine
output gear 55 to rotate together with the second rotary electric machine
output gear 55 via a second rotor shaft to which the second rotor Ro2 is
fixed.

[0051] As shown in FIG. 2, the first rotary electric machine MG1 is
electrically connected to an electricity accumulation device B via a
first inverter 4, and the second rotary electric machine MG2 is
electrically connected to the electricity accumulation device B via a
second inverter 5. Various types of electricity accumulation devices
known in the art such as a battery and a capacitor may be used as the
electricity accumulation device B. In the embodiment, each of the first
rotary electric machine MG1 and the second rotary electric machine MG2
can function both as a motor (electric motor) that is supplied with
electric power from the electricity accumulation device B to generate
power (torque) and as a generator (electric generator) that is supplied
with power to generate electric power and supply the generated electric
power to the electricity accumulation device B.

[0052] The friction engagement device CL includes two engagement members,
and selectively drivably couples a member drivably coupled to a first
engagement member CLa, which is one of the two engagement members, and a
member drivably coupled to a second engagement member CLb, which is the
other engagement member, to each other. In the embodiment, the friction
engagement device CL is formed as a wet multi-plate clutch that operates
on a hydraulic pressure. In the embodiment, the friction engagement
device CL is capable of releasing the drivable connection between the
input member I and the corresponding rotary element (in the example, the
second rotary element e2) of the differential gear device DG. That is, in
the embodiment, the friction engagement device CL is provided on a power
transfer path between the input member I and the corresponding rotary
element (in the example, the second rotary element e2) of the
differential gear device DG. The first engagement member CLa serves as an
input-side engagement member drivably coupled to the input member I to
rotate together with the input member I. The second engagement member CLb
serves as an output-side engagement member drivably coupled to the second
rotary element coupling member 42 to rotate together with the second
rotary element coupling member 42. In the embodiment, the friction
engagement device CL corresponds to the "engagement device" according to
the present invention.

[0053] In the embodiment, as shown in FIG. 1, the first rotary electric
machine MG1 is drivably coupled to the sun gear s (first rotary element
e1), the input member I is drivably coupled to the carrier ca (second
rotary element e2), and the second rotary electric machine MG2 and the
output member O are drivably coupled to the ring gear r (third rotary
element e3), via no other rotary element of the planetary gear mechanism
PG (differential gear device DG). That is, in the embodiment, the second
rotary electric machine MG2 is drivably coupled to the ring gear r (third
rotary element e3), which is the rotary element of the differential gear
device DG to which the output member O is drivably coupled, via no other
rotary element of the differential gear device DG.

[0054] Specifically, a first rotor shaft to which the first rotor Ro1 is
fixed is drivably coupled to the first rotary element coupling member 41
to rotate together with the first rotary element coupling member 41 so
that the first rotary electric machine MG1 is drivably coupled to the sun
gear s. That is, in the embodiment, the rotational speed of the sun gear
s (first rotary element e1) is equal to the rotational speed of the first
rotor Ro1 (first rotary electric machine MG1) at all times.

[0055] The input member I is drivably coupled to the first engagement
member CLa of the friction engagement device CL to rotate together with
the first engagement member CLa in order to be selectively drivably
coupled to the carrier ea via the friction engagement device CL. That is,
in the embodiment, in the case where the friction engagement device CL is
in a directly engaged state, the rotational speed of the carrier ca
(second rotary element e2) is equal to the rotational speed of the input
member I (internal combustion engine E). In the embodiment, in addition,
the difference in rotational speed between the two engagement members of
the friction engagement device CL is the difference between the
rotational speed of the input member I (internal combustion engine E) and
the rotational speed of the carrier ca (second rotary element coupling
member 42).

[0056] The second rotary electric machine MG2 and the output member O are
drivably coupled to the ring gear r via a counter gear mechanism C. As
shown in FIG. 1, the counter gear mechanism C is formed to include a
first counter gear 53, a second counter gear 54, and a counter shaft that
couples the first counter gear 53 and the second counter gear 54 so that
the first counter gear 53 and the second counter gear 54 rotate together.
The third rotary element coupling member 43 includes a counter drive gear
52 that meshes with the first counter gear 53. The second rotary electric
machine MG2 is drivably coupled to the ring gear r with the second rotary
electric machine output gear 55 disposed to mesh with the first counter
gear 53 at a position that is different in the circumferential direction
(in the circumferential direction of the first counter gear 53) from the
counter drive gear 52. The output member O is disposed to mesh with the
second counter gear 54 to be drivably coupled to the ring gear r. That
is, in the embodiment, the respective rotational speeds of the ring gear
r, the second rotary electric machine MG2, and the output member O are
proportional to each other, and the proportionality coefficient (that is,
the ratio in rotational speed) is determined in accordance with the
number of teeth of gears interposed therebetween.

[0057] The vehicle drive device 1 configured as described above can
execute a hybrid travel mode (split travel mode) in which the vehicle is
run using output torque of both the internal combustion engine E and the
rotary electric machines MG1 and MG2 and an electric travel mode (EV
travel mode) in which the vehicle is run using only output torque of the
rotary electric machines MG1 and MG2 (in the example, only output torque
of the second rotary electric machine MG2). In the hybrid travel mode,
the friction engagement device CL is brought into the directly engaged
state, and the planetary gear mechanism PG distributes output torque of
the internal combustion engine E to the sun gear s (first rotary electric
machine MG1) and the ring gear r (counter drive gear 52). In the EV
travel mode, the friction engagement device CL is brought into a
disengaged state, and the internal combustion engine E is stopped. In
addition, the rotational speed of the internal combustion engine output
shaft (input member I) basically becomes zero because of a fiction force
produced inside the internal combustion engine E, and the rotational
speed of the first rotary electric machine MG1 is basically controlled to
zero.

[0058] 1-2. System Configuration of Vehicle Drive Device

1-2-1. Overall Configuration of System

[0059] As shown in FIG. 2, the control device 70 according to the
embodiment includes a rotary electric machine control section 71, a
travel mode decision section 73, a rotational direction determination
section 81, a rotation reducing torque control section 82, and a
connection release command section 83.

[0060] The control device 70 includes an arithmetic processing unit such
as a CPU serving as a core, a storage device such as a RAM and a ROM, and
so forth. The various functional sections of the control device 70 are
formed by software (a program) stored in the ROM or the like, hardware
such as a separately provided arithmetic circuit, or a combination of
both. The functional sections are configured to exchange information
between each other.

[0061] The control device 70 is configured to acquire information from
sensors or the like provided in various portions of the vehicle
incorporating the vehicle drive device 1 in order to acquire information
on the various portions of the vehicle. Specifically, as shown in FIG. 2,
the control device 70 is configured to acquire information from an input
member sensor Se1, an output member sensor Se3, an accelerator operation
amount sensor Se11, a brake operation sensor Se12, a first rotor shaft
sensor Se2, a rotary element-to-be-released sensor Se4, and an
electricity accumulation state sensor Se10.

[0062] The input member sensor Se1 detects the rotational speed of the
input member I. In the example, the rotational speed of the input member
I detected by the input member sensor Se1 is equal to the rotational
speed of the internal combustion engine E. The output member sensor Se3
detects the rotational speed of the output member O. In the example, the
rotational speed of the output member O is proportional to the rotational
speed of the second rotary electric machine MG2. Therefore, the
rotational speed of the output member O may be acquired on the basis of
the results of detection performed by a rotation sensor (such as a
resolver) provided in the second rotary electric machine MG2. The control
device 70 derives the vehicle speed on the basis of the rotational speed
of the output member O detected by the output member sensor Se3. The
accelerator operation amount sensor Se11 detects the amount of operation
of an accelerator pedal 90 to detect the accelerator operation amount.
The electricity accumulation state sensor Se10 detects the state (such as
accumulated electricity amount and temperature) of the electricity
accumulation device B.

[0063] The brake operation sensor Se12 detects the amount of operation of
the brake pedal 91. The vehicle includes a brake device control unit 8
that controls operation of the brake device 93 (see FIG. 1). The control
device 70 controls the brake device control unit 8 such that a braking
force matching the amount of operation of the brake pedal 91 is applied
to the wheels W on the basis of the results of detection performed by the
brake operation sensor Se12.

[0064] The first rotor shaft sensor Se2 detects the rotational speed of
the first rotary electric machine MG1 (first rotor shaft). In the
example, the rotational speed of the first rotary electric machine MG1
detected by the first rotor shaft sensor Se2 is equal to the rotational
speed of the first rotary element coupling member 41 (sun gear s). The
first rotor shaft sensor Se2 may be formed by a rotation sensor (such as
a resolver) provided in the first rotary electric machine MG1, for
example.

[0065] The rotary element-to-be-released sensor Se4 detects the rotational
speed of a rotary element to be released en among the rotary elements of
the differential gear device DG. The rotary element to be released en is
the rotary element for which the friction engagement device CL is capable
of releasing drivable connection with the corresponding one of the input
member I, the output member O, and the first rotary electric machine MG1.
In the embodiment, the carrier ca serves as the rotary element to be
released en, and the rotary element-to-be-released sensor Se4 detects the
rotational speed of the second rotary element coupling member 42.

[0066] As shown in FIG. 2, the vehicle includes an internal combustion
engine control unit 3. The internal combustion engine control unit 3
controls various portions of the internal combustion engine E to control
operation of the internal combustion engine E. Specifically, the internal
combustion engine control unit 3 controls operation of the internal
combustion engine E by setting target operation points (target torque and
target rotational speed) serving as control targets for operation points
(output torque and rotational speed) of the internal combustion engine E
and causing the internal combustion engine E to operate in accordance
with the control targets. The target torque and the target rotational
speed are set on the basis of a command from the control device 70. In
the case where a command to start the internal combustion engine E is
received from the control device 70 when the internal combustion engine E
is stopped, the internal combustion engine control unit 3 starts fuel
injection and ignition to start the internal combustion engine E. In the
case where a command to stop the internal combustion engine E is received
from the control device 70 after the internal combustion engine E is
started (when the internal combustion engine E is in operation), the
internal combustion engine control unit 3 stops fuel injection and
ignition to stop the internal combustion engine E.

[0067] As shown in FIG. 2, the vehicle also includes a friction engagement
device control unit 6 that controls operation of the friction engagement
device CL. In the embodiment, the friction engagement device CL operates
on a hydraulic pressure, and the friction engagement device control unit
6 controls operation of the friction engagement device CL by controlling
a hydraulic pressure control device 2. Specifically, the friction
engagement device control unit 6 generates a hydraulic pressure command
value for the friction engagement device CL, and controls the hydraulic
pressure control device 2 such that a hydraulic pressure corresponding to
the hydraulic pressure command value is supplied to the friction
engagement device CL.

[0068] The state of the friction engagement device CL includes a "coupled
state" in which the drivable connection made by the friction engagement
device CL is maintained and a "decoupled state" in which the drivable
connection made by the friction engagement device CL is released. That
is, in the "coupled state", torque is transferred via the friction
engagement device CL, and the drivable connection made by the friction
engagement device CL is enabled. In the "decoupled state", meanwhile,
torque is not transferred via the friction engagement device CL, and the
drivable connection made by the friction engagement device CL is
disabled.

[0069] In the embodiment, the state of the friction engagement device CL
is switched between the coupled state and the decoupled state in
accordance with the state of engagement between the two engagement
members provided in the friction engagement device CL. That is, the
friction engagement device CL is brought into the decoupled state in the
case where the state of engagement between the two engagement members is
a "disengaged state", and the friction engagement device CL is brought
into the coupled state in the case where the state of engagement between
the two engagement members is a "slip engagement state" or a "directly
engaged state".

[0070] The "disengaged state" is a state (engagement released state) in
which rotation and torque are not transferred between the two engagement
members of the friction engagement device CL. The "slip engagement state"
is a state (engaged state) in which the two engagement members are
engaged with each other with a difference in rotational speed
therebetween. The "directly engaged state" is a state (engaged state) in
which the two engagement members rotate together, That is, the "slip
engagement state" is an engaged state in which torque is transferred
between the two engagement members of the friction engagement device CL
with the two engagement members rotatable relative to each other.
Meanwhile, the "directly engaged state" is an engaged state in which the
two engagement members of the friction engagement device CL are directly
coupled to each other so that there is no difference in rotation between
the two engagement members. Thus, the engaged state includes the slip
engagement state and the directly engaged state. The directly engaged
state includes a "steady directly engaged state" in which the directly
engaged state is maintained regardless of fluctuations in torque
transferred by the friction engagement device CL. Such a steady directly
engaged state is obtained at a line pressure (reference hydraulic
pressure) generated by the hydraulic pressure control device 2, for
example. In the following description, the state of the friction
engagement device CL is represented in relation to the state of
engagement between the two engagement members.

[0071] The magnitude of torque that can be transferred between the two
engagement members of the friction engagement device CL is decided in
accordance with the engagement pressure of the friction engagement device
CL at that time point. The magnitude of torque at this time is defined as
the transfer torque capacity of the friction engagement device CL. In the
embodiment, increase and decrease in transfer torque capacity of the
friction engagement device CL can be continuously controlled by
continuously controlling the magnitudes of the amount of oil and the
hydraulic pressure to be supplied to the friction engagement device CL
through a proportional solenoid valve in accordance with the hydraulic
pressure command value for the friction engagement device CL. In the
embodiment, the friction engagement device control unit 6 controls the
state of the friction engagement device CL by controlling the transfer
torque capacity of the friction engagement device CL on the basis of an
engagement command, an engagement release command (disengagement
command), and so forth from the control device 70.

[0072] 1-2-2. Configuration of Travel Mode Decision Section

[0073] The travel mode decision section 73 is a functional section that
decides a travel mode of the vehicle. The travel mode decision section 73
decides the travel mode to be established by the vehicle drive device 1
on the basis of the vehicle speed derived on the basis of the results of
detection performed by the output member sensor Se3, the accelerator
operation amount detected by the accelerator operation amount sensor
Se11, and the electricity accumulation state (such as accumulated
electricity amount and temperature) detected by the electricity
accumulation state sensor Se10, for example. In the embodiment, examples
of the travel mode that can be decided by the travel mode decision
section 73 include the electric travel mode and the hybrid travel mode.
The travel mode decision section 73 basically references a mode selection
map (not shown) stored in a storage device formed by a memory or the like
and defining the relationship between the vehicle speed, the accelerator
operation amount, and the electricity accumulation state and the travel
mode to decide the travel mode.

[0074] According to the mode selection map, it is decided to transition
into the electric travel mode in the case where internal combustion
engine stop conditions are established during travel in the hybrid travel
mode. The internal combustion engine stop conditions are conditions for
stopping the internal combustion engine E which has been started (in
operation), and are established in the case where the vehicle does not
need torque of the internal combustion engine E any more and in the case
where the vehicle cannot utilize torque of the internal combustion engine
E. For example, the internal combustion engine stop conditions are
established in the case where torque required by the vehicle can be
obtained with only the rotary electric machines MG1 and MG2 during travel
in the hybrid travel mode because the amount of depression of the
accelerator pedal 90 is decreased, the amount of depression of the brake
pedal 91 is increased, or the like. The internal combustion engine stop
conditions are also established in the case where it is no longer
necessary that the rotary electric machines MG1 and MG2 should generate
electricity using torque of the internal combustion engine E to charge
the electricity accumulation device B because the amount of electricity
accumulated in the electricity accumulation device B has recovered to a
threshold determined in advance or more.

[0076] The rotary electric machine control section 71 is a functional
section that controls operation of the first rotary electric machine MG1
and the second rotary electric machine MG2. Specifically, the rotary
electric machine control section 71 sets target operation points (target
torque and target rotational speed) serving as control targets for
operation points (output torque and rotational speed) of the first rotary
electric machine MG1, and controls the first inverter 4 such that the
first rotary electric machine MG1 operates in accordance with the control
targets. In the example, the rotary electric machine control section 71
controls operation of the first rotary electric machine MG1 through
torque control or rotational speed control. In the torque control, target
torque for the first rotary electric machine MG1 is set to match output
torque of the first rotary electric machine MG1 with the target torque.
In the rotational speed control, meanwhile, a target rotational speed for
the first rotary electric machine MG1 is set to match the rotational
speed of the first rotary electric machine MG1 with the target rotational
speed. Control for the second rotary electric machine MG2 is the same as
the control for the first rotary electric machine MG1 except that the
first inverter 4 is replaced with the second inverter 5.

[0077] In the embodiment, the torque control described above includes
rotation reducing torque control in which the first rotary electric
machine MG1 is caused to output rotation reducing torque. The rotation
reducing torque control is executed by the rotation reducing torque
control section 82. The configuration of the rotation reducing torque
control section 82 will be described later in "1-2-5. Configuration of
Rotation Reducing Torque Control Section".

[0079] The rotational direction determination section 81 is a functional
section that executes rotational direction determination when the
internal combustion engine stop conditions for stopping the internal
combustion engine E are established in a state in which the drivable
connection made by the friction engagement device CL is maintained, the
internal combustion engine E is in operation, and the output member O is
rotating. That is, the rotational direction determination section 81
executes rotational direction determination when the internal combustion
engine stop conditions are established during travel with the friction
engagement device CL in the engaged state (basically the directly engaged
state) and with the internal combustion engine E started (during travel
in the hybrid travel mode). The determination as to whether or not the
internal combustion engine stop conditions are established is executed by
the control device 70.

[0080] In the "rotational direction determination", it is determined
whether or not the rotational direction of the first rotary electric
machine MG1 at the time when the internal combustion engine stop
conditions are established (hereinafter referred to as "stop condition
establishing rotational direction K1") is opposite to the rotational
direction of the first rotary electric machine MG1 at an operation point
at which the rotational speed of the internal combustion engine E becomes
zero (hereinafter referred to as "subject rotational direction K2").

[0081] The rotational direction determination executed by the rotational
direction determination section 81 will be described with reference to
FIG. 3. FIG. 3 is a velocity diagram representing the state of operation
of the differential gear device DG (in the example, the planetary gear
mechanism PG). In the velocity diagram, the vertical axis corresponds to
the rotational speed of each rotary element. That is, the indication "0"
provided on the vertical axis indicates that the rotational speed is
zero, with the upper side corresponding to positive rotation (the
rotational speed is positive) and the lower side corresponding to
negative rotation (the rotational speed is negative). The term "positive
direction" as used for the direction of rotation (rotational speed) and
torque of each member indicates the same direction as the rotational
direction of the internal combustion engine E during operation of the
internal combustion engine E. The term "negative direction" indicates the
opposite direction.

[0082] A plurality of vertical lines disposed in parallel correspond to
the respective rotary elements of the differential gear device DG. The
intervals between the vertical lines corresponding to the respective
rotary elements correspond to a gear ratio λ of the differential
gear device DG. In the example, the differential gear device DG is formed
by the planetary gear mechanism PG, and the gear ratio λ. is the
ratio in number of teeth between the sun gear s and the ring gear r. The
reference symbols "Em", "Ei", and "Eo" enclosed in boxes provided above
the vertical lines indicate a reaction force transfer element Em, an
input rotary element Ei, and an output rotary element Eo, respectively,
for execution of the hybrid travel mode. The first rotary electric
machine MG1, the internal combustion engine E (input member I), and the
output member O are drivably coupled to the reaction force transfer
element Em, the input rotary element Ei, and the output rotary element
Eo, respectively, via no other rotary element of the differential gear
device DG. That is, the reaction force transfer element Em, the input
rotary element Ei, and the output rotary element Eo are a first rotary
electric machine coupling element, an input member coupling element
(internal combustion engine coupling element), and an output member
coupling element, respectively.

[0083] In the velocity diagram, the rotational speed of the first rotary
electric machine MG1, the rotational speed of the second rotary electric
machine MG2, the rotational speed of the internal combustion engine E
(input member I), and the rotational speed of the output shaft O are
indicated by symbols that are different from each other. Specifically,
the "circular" symbols indicate the rotational speed of the first rotary
electric machine MG1, the "square" symbol indicates the rotational speed
of the second rotary electric machine MG2, the "triangular" symbols
indicate the rotational speed of the internal combustion engine E, and
the "star" symbol indicates the rotational speed of the output member O.
In order to facilitate understanding of the present invention, the
rotational speed of each of the first rotary electric machine MG1, the
second rotary electric machine MG2, the internal combustion engine E, and
the output member O represents a rotational speed after conversion (speed
change) of rotational speed performed by transmission members (excluding
an engagement element that selectively transfers rotation and torque such
as the friction engagement device CL) provided on the power transfer path
to the corresponding rotary element (rotary element coupling member) of
the differential gear device DG. Also in the following description, the
rotational speed of each member basically means a rotational speed after
conversion of rotational speed performed by the transmission members.

[0084] Specifically, in the embodiment, the first rotary electric machine
MG1 is drivably coupled to the first rotary element coupling member 41 to
rotate together with the first rotary element coupling member 41.
Therefore, the rotational speed of the first rotary electric machine MG1
(sun gear s) in the velocity diagram coincides with the actual rotational
speed of the first rotary electric machine MG1. In the case where the
friction engagement device CL is in the directly engaged state, the
internal combustion engine E (input member I) rotates at the same
rotational speed as the second rotary element coupling member 42.
Therefore, the rotational speed of the internal combustion engine E
(carrier ca) in the velocity diagram coincides with the actual rotational
speed of the internal combustion engine E.

[0085] Meanwhile, the second rotary electric machine MG2 is drivably
coupled to the third rotary element coupling member 43 via the counter
gear mechanism C. Therefore, the rotational speed of the second rotary
electric machine MG2 (ring gear r) in the velocity diagram is obtained by
multiplying the actual rotational speed of the second rotary electric
machine MG2 by the gear ratio of a power transfer system formed by the
second rotary electric machine output gear 55, the first counter gear 53,
and the counter drive gear 52. Likewise, the output member O is drivably
coupled to the third rotary element coupling member 43 via the counter
gear mechanism C. Therefore, the rotational speed of the output member O
in the velocity diagram is obtained by multiplying the actual rotational
speed of the output member O by the gear ratio of a power transfer system
formed by the differential input gear (output member O), the second
counter gear 54, the first counter gear 53, and the counter drive gear
52.

[0086] "T1" indicates torque (first rotary electric machine torque)
transferred from the first rotary electric machine MG1 to the
corresponding rotary element (reaction force transfer element Em; in the
example, the sun gear s) of the differential gear device DG. "T2"
indicates torque (second rotary electric machine torque) transferred from
the second rotary electric machine MG2 to the corresponding rotary
element (in the example, the ring gear r) of the differential gear device
DG. "TE" indicates torque (internal combustion engine torque) transferred
from the internal combustion engine E to the corresponding rotary element
(input rotary element Ei; in the example, the carrier ca) of the
differential gear device DG. "To" indicates torque (travel torque, travel
resistance) transferred from the output member O (wheels W) to the
corresponding rotary element (output rotary element Eo; in the example,
the ring gear r) of the differential gear device DG. An arrow provided
adjacent to each torque represents the direction of each torque applied
during execution of the hybrid travel mode. An arrow pointing upward
represents torque in the positive direction. An arrow pointing downward
represents torque in the negative direction. Each velocity diagram to be
referenced below also indicates the state of operation of the
differential gear device DG as with FIG. 3.

[0087] The state indicated by the thick solid line in FIG. 3 (the state
indicated by "(1)") represents a state of operation in the hybrid travel
mode. In the hybrid travel mode, the friction engagement device CL is
brought into the engaged state (basically the directly engaged state). In
the hybrid travel mode, the internal combustion engine E outputs torque
in the positive direction matching the required drive force for driving
the vehicle while being controlled so as to be maintained in a state with
high efficiency and low gas emission (a state according to optimum fuel
consumption characteristics), and the first rotary electric machine MG1
functions to receive a reaction force of torque of the internal
combustion engine E by outputting torque in the negative direction. In
this event, the first rotary electric machine MG1 basically rotates
positively to generate electricity. Meanwhile, the second rotary electric
machine MG2 basically outputs torque in the positive direction to
supplement torque to be transferred to the output member O. In the
embodiment, the output member O basically rotates in the positive
direction as with the internal combustion engine E during execution of
the hybrid travel mode.

[0088] In the case where the internal combustion engine stop conditions
are established in the state indicated by the thick solid line in FIG. 3,
the rotational direction determination section 81 executes the rotational
direction determination. In the example shown in FIG. 3, the operation
point of the first rotary electric machine MG1 at the time when the
internal combustion engine stop conditions are established is indicated
by the thick solid circle in FIG. 3. Therefore, the stop condition
establishing rotational direction K1 is the "positive direction". The
stop condition establishing rotational direction K1 is acquired on the
basis of the results of detection performed by the first rotor shaft
sensor Se2, for example. The rotational speed of the first rotary
electric machine MG1 (the rotational speed of the sun gear s) is uniquely
determined in accordance with the rotational speed of the carrier ca and
the rotational speed of the ring gear r. Therefore, the stop condition
establishing rotational direction K1 may be derived on the basis of the
respective detected rotational speeds of the carrier ca and the ring gear
r.

[0089] In the example shown in FIG. 3, the operation point of the first
rotary electric machine MG1 at which the rotational speed of the internal
combustion engine E becomes zero with the friction engagement device CL
in the directly engaged state is indicated by the thin broken circle in
FIG. 3, at which the rotational speed is a subject rotational speed Ns.
Therefore, the subject rotational direction K2 is the "negative
direction". Hence, in the example shown in FIG. 3, it is determined that
the stop condition establishing rotational direction K1 is opposite to
the subject rotational direction K2. Although not shown, the stop
condition establishing rotational direction K1 may be in the "negative
direction" depending on the rotational speed of the internal combustion
engine E and the rotational speed of the output member O. In this case,
it is determined that the stop condition establishing rotational
direction K1 is the same as the subject rotational direction K2. In each
of the drawings (FIGS. 7 and 9 to 15) to be referenced later in relation
to other embodiments, a case where the stop condition establishing
rotational direction K1 is opposite to the subject rotational direction
K2 is shown as the state during execution of the hybrid travel mode (the
state indicated by the thick solid line).

[0090] The relationship between the subject rotational direction K2 and
the rotational direction of the output member O is determined in
accordance with the order of the respective rotational speeds of the
reaction force transfer element Em, the input rotary element Ei, and the
output rotary element Eo. That is, in the case where the rotational speed
of the input rotary element Ei comes between the respective rotational
speeds of the other two of the three rotary elements as in the coupling
relationship shown in FIG. 3, for example, the subject rotational
direction K2 is opposite to the rotational direction of the output member
O. In the case where the rotational speed of the input rotary element Ei
does not come between the respective rotational speeds of the other two
of the three rotary elements as in the coupling relationship shown in
FIG. 10 to be referenced later, for example, the subject rotational
direction K2 is the same as the rotational direction of the output member
O.

[0091] In the embodiment, the order of the respective rotational speeds of
the reaction force transfer element Em, the input rotary element Ei, and
the output rotary element Eo is determined such that the rotational speed
of the input rotary element Ei comes between the respective rotational
speeds of the other two. Therefore, the subject rotational direction K2
is opposite to the rotational direction of the output member O. In the
embodiment, as described above, the output member O basically rotates in
the positive direction as with the internal combustion engine E during
execution of the hybrid travel mode. Therefore, in the embodiment, the
subject rotational direction K2 is basically the negative direction.
Hence, in the embodiment, it is determined in the rotational direction
determination made by the rotational direction determination section 81
that the stop condition establishing rotational direction K1 is opposite
to the subject rotational direction K2 in the case where the stop
condition establishing rotational direction K1 is the positive direction,
and that the stop condition establishing rotational direction K1 is the
same as the subject rotational direction K2 in the case where the stop
condition establishing rotational direction K1 is the negative direction.

[0093] The rotation reducing torque control section 82 is a functional
section that executes the rotation reducing torque control in which the
first rotary electric machine MG1 is caused to output rotation reducing
torque in the direction to reduce the rotational speed of the internal
combustion engine E on condition that the rotational direction
determination section 81 determines that the stop condition establishing
rotational direction K1 is opposite to the subject rotational direction
K2. The state indicated by the thin spaced broken line (thin dotted line)
in FIG. 3 (the state indicated by "(2)") represents a state in which the
rotational speed of the internal combustion engine E is reduced compared
to that during travel in the hybrid travel mode through execution of the
rotation reducing torque control.

[0094] In the embodiment, a command for the internal combustion engine
control unit 3 to stop the internal combustion engine E is immediately
executed when the internal combustion engine stop conditions are
established. The rotation reducing torque control section 82 basically
starts the rotation reducing torque control with at least one (in the
example, both) of fuel injection and ignition of the internal combustion
engine E stopped. Immediately after fuel injection and ignition of the
internal combustion engine E are stopped, the internal combustion engine
output shaft of the internal combustion engine E is subjected to inertial
torque matching the moment of inertia of the internal combustion engine E
in the direction to continuously rotate (positive direction). During
execution of the rotation reducing torque control, the first rotary
electric machine MG1 is controlled so as to output the rotation reducing
torque which is torque for reducing the rotational speed of the internal
combustion engine E against the inertial torque. To "reduce" a rotational
speed means to vary the rotational speed in the negative direction, and
to "increase" a rotational speed means to vary the rotational speed in
the positive direction.

[0095] During execution of the hybrid travel mode, the first rotary
electric machine MG1 functions to receive a reaction force of the
internal combustion engine E. To this end, the first rotary electric
machine MG1 outputs torque in the direction to reduce the rotational
speed of the internal combustion engine E. Therefore, the direction of
the rotation reducing torque output from the first rotary electric
machine MG1 during execution of the rotation reducing torque control
coincides with the direction of output torque of the first rotary
electric machine MG1 during execution of the hybrid travel mode. The
direction of output torque of the first rotary electric machine MG1
during execution of the hybrid travel mode is determined in accordance
with the order of the respective rotational speeds of the reaction force
transfer element Em, the input rotary element Ei, and the output rotary
element Eo. That is, in the case where the rotational speed of the output
rotary element Eo does not come between the respective rotational speeds
of the other two of the three rotary elements, the direction of the
output torque is the negative direction. In the case where the rotational
speed of the output rotary element Eo comes between the respective
rotational speeds of the other two of the three rotary elements,
meanwhile, the direction of the output torque is the positive direction.

[0096] In the embodiment, the order of the respective rotational speeds of
the reaction force transfer element Em, the input rotary element Ei, and
the output rotary element Eo is determined such that the rotational speed
of the output rotary element Eo does not come between the respective
rotational speeds of the other two, and therefore the direction of the
rotation reducing torque is the negative direction. Therefore, the first
rotary electric machine MG1 is controlled so as to output torque in the
negative direction (rotation reducing torque) so that the rotational
speed of the first rotary electric machine MG1 is reduced during
execution of the rotation reducing torque control, which reduces the
rotational speed of the first rotary electric machine MG1 and the
rotational speed of the internal combustion engine E.

[0097] In the embodiment, as described above, in the case where the stop
condition establishing rotational direction K1 is the positive direction,
the rotational direction determination section 81 determines that the
stop condition establishing rotational direction K1 is opposite to the
subject rotational direction K2. Therefore, at the start of execution of
the rotation reducing torque control, execution of which is started on
condition of such a determination, the direction of the rotation reducing
torque is opposite to the rotational direction of the first rotary
electric machine MG1 (that is, in the direction to generate electricity).
Hence, execution of the rotation reducing torque control enables the
first rotary electric machine MG1 to regenerate (generate) electric power
matching the magnitude of the inertial torque of the internal combustion
engine E during a period until the rotational speed of the first rotary
electric machine MG1 becomes zero.

[0098] In the embodiment, the rotation reducing torque control is stopped
before the rotational direction of the first rotary electric machine MG1
becomes the same as the subject rotational direction K2. In the example,
the subject rotational direction K2 is the negative direction, and
therefore the rotation reducing torque control is stopped before the
rotational speed of the first rotary electric machine MG1 becomes
negative, that is, with the rotational speed of the first rotary electric
machine MG1 equal to or more than zero.

[0099] The rotation reducing torque may be set in accordance with the
target rate of variation in rotational speed of the internal combustion
engine E, the moment of inertia of the internal combustion engine E, the
gear ratio λ of the differential gear device DG, and so forth
during execution of the rotation reducing torque control. Specifically,
the magnitude of the rotation reducing torque output from the first
rotary electric machine MG1 is set such that the carrier ca is subjected
to torque with a magnitude matching the product of the target rate of
variation in rotational speed of the internal combustion engine E and the
moment of inertia of the internal combustion engine E. The rotation
reducing torque may be a fixed value set in advance, or may be set to be
variable in accordance with the state of operation during execution of
the hybrid travel mode. In this event, the rotation reducing torque may
be set to become larger as the rotational speed of the internal
combustion engine E becomes higher during execution of the hybrid travel
mode, for example.

[0100] In the embodiment, the rotary electric machine control section 71
is configured to execute fluctuation suppressing control at least during
a period since the internal combustion engine stop conditions are
established until the drivable connection made by the friction engagement
device CL is released. In the fluctuation suppressing control, the second
rotary electric machine MG2 is caused to output fluctuation suppressing
torque for suppressing torque fluctuations to be transferred to the
output member O via the differential gear device DG because of variations
in state of operation (such as rotational speed and output torque) of the
first rotary electric machine MG1 and variations in state of engagement
of the friction engagement device CL. The fluctuation suppressing torque
will be derived by a fluctuation suppressing torque derivation section 84
to be described later in "1-2-7. Configuration of Fluctuation Suppressing
Torque Derivation Section".

[0101] 1-2-6. Configuration of Connection Release Command Section

[0102] The connection release command section 83 is a functional section
that issues a command to release the drivable connection made by the
friction engagement device CL on condition that the rotational speed of
the first rotary electric machine MG1 falls within a connection release
rotational speed range A. In the embodiment, the drivable connection made
by the friction engagement device CL is released by releasing engagement
between the two engagement members of the friction engagement device CL.
Hence, in the embodiment, the connection release command section 83
issues a command to release engagement of the friction engagement device
CL on condition that the rotational speed of the first rotary electric
machine MG1 falls within the connection release rotational speed range A.

[0103] The connection release rotational speed range A is set so as to
include zero. The connection release rotational speed range A is set in
consideration of the control responsiveness of the first rotary electric
machine MG1, for example. The magnitude of the connection release
rotational speed range A is selected from a range of 50 rpm or more and
500 rpm or less, for example. In the embodiment, as shown in FIG. 3, the
connection release rotational speed range A is set so as to include a
rotational speed range in which the rotational speed is positive, and the
connection release command section 83 issues a command to release
engagement of the friction engagement device CL on condition that the
rotational speed of the first rotary electric machine MG1 becomes a
rotational speed (connection release rotational speed Ni) that is equal
to or more than zero and that is included in the connection release
rotational speed range A. Thus, in the embodiment, the engagement release
command issued by the connection release command section 83 is executed
before the rotational direction of the first rotary electric machine MG1
becomes the same as the subject rotational direction K2.

[0104] In the example shown in FIG. 3, the connection release rotational
speed range A is set so as to include a rotational speed range in which
the rotational speed is negative. However, the connection release
rotational speed range A may be set so as to include only a rotational
speed range in which the rotational speed is positive in addition to
zero. In the case where the connection release rotational speed range A
is set so as to include both a rotational speed range in which the
rotational speed is positive and a rotational speed range in which the
rotational speed is negative in addition to zero, the connection release
rotational speed range A may be set so as to include equal positive and
negative rotational speed ranges as in the example shown in FIG. 3, or
may be set so as to include non-equal positive and negative rotational
speed ranges.

[0105] The state indicated by the thin spaced broken line (thin dotted
line) in FIG. 3 (the state indicated by "(2)") represents a state in
which the rotational speed of the first rotary electric machine MG1
becomes the connection release rotational speed Ni. In the example, the
connection release rotational speed Ni is higher than zero. In this
state, the connection release command section 83 issues a command to
release engagement of the friction engagement device CL. In the
embodiment, further, the rotation reducing torque control is stopped on
condition that the rotational speed of the first rotary electric machine
MG1 becomes the connection release rotational speed Ni. That is, in the
embodiment, the rotational speed of the first rotary electric machine MG1
at which the rotation reducing torque control is stopped is equal to the
rotational speed of the first rotary electric machine MG1 at which the
connection release command section 83 issues a command to release
engagement of the friction engagement device CL.

[0106] When the connection release command section 83 issues a command to
release engagement of the friction engagement device CL, the friction
engagement device control unit 6 performs control so as to reduce the
transfer torque capacity of the friction engagement device CL at a
predetermined (for example, constant) variation rate from the current
value (for example, such a value that brings the friction engagement
device CL into the steady directly engaged state) to zero. This brings
the friction engagement device CL into the disengaged state.

[0107] When the friction engagement device CL is brought into the
disengaged state, the rotational speed of the internal combustion engine
E is varied toward zero at a variation rate matching the moment of
inertia of the internal combustion engine E; the frictional resistance
due to sliding parts, bearings, and so forth forming the internal
combustion engine E; and so forth. The rotational speed of the internal
combustion engine E becomes zero after a predetermined time elapses. In
the embodiment, the first rotary electric machine MG1 is controlled (for
example, subjected to rotational speed feedback control) such that the
rotational speed of the first rotary electric machine MG1 becomes zero
after the rotation reducing torque control is stopped, and the rotational
speed of the first rotary electric machine MG1 becomes zero after a
predetermined time elapses.

[0108] The state indicated by the thick broken line in FIG. 3 (the state
indicated by "(3)") represents a state of operation in which the vehicle
is traveling in the electric travel mode with the friction engagement
device CL in the disengaged state and with both the respective rotational
speeds of the internal combustion engine E and the first rotary electric
machine MG1 brought to zero. In the electric travel mode, the friction
engagement device CL is in the disengaged state, and therefore the rotary
element to be released en of the differential gear device DG is freely
rotatable independently of the internal combustion engine E. In the
embodiment, the carrier ca serves as the rotary element to be released
en, and rotates at a rotational speed determined on the basis of the
vehicle speed (the rotational speed of the output member O) and the
rotational speed of the first rotary electric machine MG1.

[0110] The fluctuation suppressing torque derivation section 84 is a
functional section that derives the fluctuation suppressing torque that
the second rotary electric machine MG2 is caused to output during
execution of the fluctuation suppressing control. As described above,
fluctuation suppressing control is executed at least during a period
since the internal combustion engine stop conditions are established
until the drivable connection made by the friction engagement device CL
is released.

[0111] In the case where the friction engagement device CL is in the slip
engagement state or the directly engaged state, torque fluctuations are
transferred to the output member O via the differential gear device DG
because of variations in state of operation (such as rotational speed and
output torque) of the first rotary electric machine MG1. Torque
fluctuations are also transferred to the output member O via the
differential gear device DG because of variations in state of engagement
of the friction engagement device CL. The fluctuation suppressing torque
is torque for suppressing such torque fluctuations. The direction of the
fluctuation suppressing torque is the direction to cancel the torque
fluctuations. The magnitude of the fluctuation suppressing torque is set
on the basis of the magnitude of the torque fluctuations. The rotary
electric machine control section 71 controls operation of the second
rotary electric machine MG2 by setting the target torque for the second
rotary electric machine MG2 to torque obtained by adding the fluctuation
suppressing torque to second rotary electric machine required torque
(torque required for the second rotary electric machine MG2) determined
in accordance with vehicle required torque.

[0112] 1-3. Content of Internal Combustion Engine Stop Control

[0113] The content of internal combustion engine stop control according to
the embodiment will be described with reference to FIG. 4. FIG. 4 shows
an example of a time chart of a process in which the internal combustion
engine stop control is executed during travel in the hybrid travel mode
to transition into the electric travel mode. More specifically, FIG. 4
shows an example of a time chart of a process in which the brake pedal 91
is depressed to stop the internal combustion engine and to transition
into a regeneration mode. In the "regeneration mode", which is included
in the electric travel mode, the second rotary electric machine MG2 is
caused to output torque (regenerative torque) in the direction to
generate electricity. The "internal combustion engine stop control" is a
generic term for various types of control executed by the various
sections of the control device 70 to transition into the electric travel
mode when the internal combustion engine stop conditions are established.
In FIG. 4, it is assumed that the internal combustion engine stop
conditions are established at time T0, and transition into the electric
travel mode is completed at time T3.

[0114] Until time T0, the transfer torque capacity of the friction
engagement device CL has such a value that brings the friction engagement
device CL into the steady directly engaged state, the internal combustion
engine E is in operation, and output torque of the internal combustion
engine E is distributed to the sun gear s and the ring gear r. The first
rotary electric machine MG1 functions to receive a reaction force of
torque of the internal combustion engine E by outputting torque in the
negative direction. In the example, the first rotary electric machine MG1
makes positive rotation to generate electricity. The second rotary
electric machine MG2 outputs torque in the positive direction to
supplement torque to be transferred to the output member O.

[0115] When the brake pedal 91 is depressed so that the internal
combustion engine stop conditions are established at time T0, a command
for the internal combustion engine control unit 3 to stop the internal
combustion engine E is executed, and the rotational direction
determination section 81 executes the rotational direction determination.
In the embodiment, as described above, the first rotary electric machine
MG1 makes positive rotation until time T0, and therefore it is determined
in the rotational direction determination that the stop condition
establishing rotational direction K1 is opposite to the subject
rotational direction K2. Hence, in the example, the rotation reducing
torque control section 82 executes the rotation reducing torque control.
At and after time T0, the second rotary electric machine MG2 is
controlled so as to output regenerative torque in the direction to
generate electricity (in the example, in the negative direction). In the
example, the fluctuation suppressing control is executed at least during
a period since the internal combustion engine stop conditions are
established until the drivable connection made by the friction engagement
device CL is released. Therefore, the fluctuation suppressing torque has
been added to the regenerative torque output from the second rotary
electric machine MG2 during a period until the friction engagement device
CL is brought into the disengaged state.

[0116] In the example shown in FIG. 4, execution of the rotation reducing
torque control is started at time T1 when a predetermined time elapses
from time T0. In the example, the rotation reducing torque output from
the first rotary electric machine MG1 during execution of the rotation
reducing torque control is torque in the negative direction, and
therefore execution of the rotation reducing torque control reduces the
rotational speed of the first rotary electric machine MG1 and the
rotational speed of the internal combustion engine E.

[0117] When a predetermined time elapses after the time point (time T1) at
which execution of the rotation reducing torque control is started so
that the rotational speed of the first rotary electric machine MG1
reaches the connection release rotational speed Ni which falls within the
connection release rotational speed range A (time T2), the rotation
reducing torque control is stopped, and the connection release command
section 83 issues a command to release engagement of the friction
engagement device CL. When a command to release engagement of the
friction engagement device CL is issued, the friction engagement device
control unit 6 performs control so as to reduce the transfer torque
capacity of the friction engagement device CL at a constant variation
rate from the current value (such a value that brings the friction
engagement device CL into the steady directly engaged state) to zero. As
shown in FIG. 4, the regenerative torque output from the second rotary
electric machine MG2 is varied in accordance with the fluctuation
suppressing torque which is varied along with the transfer torque
capacity of the friction engagement device CL. When the rotation reducing
torque control is stopped, the first rotary electric machine MG1 is
subjected to rotational speed feedback control such that the rotational
speed of the first rotary electric machine MG1 becomes zero. At time T3,
the rotational speed of the first rotary electric machine MG1 becomes
zero. In the example, the rotational speed of the internal combustion
engine E also becomes zero at time T3.

[0119] Next, the process procedures of the internal combustion engine stop
control according to the embodiment will be described with reference to
the flowchart of FIG. 5. The process procedures described below are
executed by the various functional sections of the control device 70. In
the case where the functional sections are configured by a program, the
arithmetic processing unit provided in the control device 70 operates as
a computer that executes the program configuring the functional sections
described above.

[0120] When the internal combustion engine stop conditions are established
(step #02: Yes) during travel in the hybrid travel mode (step #01: Yes),
a command for the internal combustion engine control unit 3 to stop the
internal combustion engine E is executed (step #03), and the rotational
direction determination section 81 makes a determination (rotational
direction determination) as to whether or not the stop condition
establishing rotational direction K1 is opposite to the subject
rotational direction K2 (step #04). Steps #03 and #04 may be executed in
parallel at the same time, or one of the steps may be executed first and
the other may be executed thereafter.

[0121] If it is determined in step #04 that the stop condition
establishing rotational direction K1 is opposite to the subject
rotational direction K2 (step #04: Yes), the rotation reducing torque
control section 82 starts the rotation reducing torque control (step
#05). Execution of the rotation reducing torque control is continued
during a period until the rotational speed of the first rotary electric
machine MG1 reaches the connection release rotational speed Ni set within
the connection release rotational speed range A (step #06: No). When it
is stated that a subject rotational speed (for example, the rotational
speed of the first rotary electric machine MG1) "reaches" a target value
(target rotational speed), it is meant that the difference in rotational
speed between the subject rotational speed and the target value becomes
less than a target reach determination threshold. The target reach
determination threshold is set to a value of 10 rpm or more and 100 rpm
or less, for example.

[0122] When the rotational speed of the first rotary electric machine MG1
reaches the connection release rotational speed Ni (step #06: Yes), the
rotation reducing torque control is terminated (stopped) (step #07), and
a command to release connection of the friction engagement device CL (in
the example, a command to release engagement of the friction engagement
device CL) issued by the connection release command section 83 is
executed (step #08). Steps #07 and #08 may be executed in parallel at the
same time, or one of the steps may be executed first and the other may be
executed thereafter.

[0123] If it is determined in step #04 that the stop condition
establishing rotational direction K1 is not opposite to (that is, is the
same as) the subject rotational direction K2 (step #04: No), the process
proceeds to step #08, where a command to release engagement of the
friction engagement device CL issued by the connection release command
section 83 is executed. Thereafter, in the embodiment, the first rotary
electric machine MG1 is controlled (for example, subjected to rotational
speed feedback control) such that the rotational speed of the first
rotary electric machine MG1 becomes zero.

2. Second Embodiment

[0124] Next, a vehicle drive device according to a second embodiment of
the present invention will be described with reference to FIGS. 6 and 7.
As shown in FIG. 6, the vehicle drive device 1 according to the
embodiment is basically configured in the same manner as that according
to the first embodiment described above except for the position at which
the friction engagement device CL is disposed. The differences between
the configuration of the vehicle drive device 1 according to the
embodiment and that according to the first embodiment described above
will be mainly described below. The same elements as those in the first
embodiment described above will not be specifically described.

[0125] In the vehicle drive device 1 according to the embodiment, as shown
in FIG. 6, the friction engagement device CL is provided on a power
transfer path between the output member O and the corresponding rotary
element (third rotary element e3) of the differential gear device DG,
rather than between the input member I and the corresponding rotary
element (second rotary element e2) of the differential gear device DG.
This makes the differential gear device DG capable of releasing the
drivable connection between the output member O and the corresponding
rotary element (third rotary element e3) of the differential gear device
DG.

[0126] Specifically, the counter drive gear 52 is drivably coupled to the
first engagement member CLa, which is one of the engagement members of
the friction engagement device CL, to rotate together with the first
engagement member CLa, and the third rotary element coupling member 43 is
drivably coupled to the second engagement member CLb, which is the other
engagement member of the friction engagement device CL, to rotate
together with the second engagement member CLb. Hence, the friction
engagement device CL is also positioned on a power transfer path between
the second rotary electric machine MG2 and the corresponding rotary
element (third rotary element e3) of the differential gear device DG, and
the drivable connection between the second rotary electric machine MG2
and the corresponding rotary element (third rotary element e3) of the
differential gear device DG is released by bringing the friction
engagement device CL into the disengaged state in addition to the
drivable connection between the output member O and the corresponding
rotary element (third rotary element e3) of the differential gear device
DG.

[0127] In the embodiment, the ring gear r serves as the rotary element to
be released en, Therefore, as shown in FIG. 6, the rotary
element-to-be-released sensor Se4 is disposed so as to be able to detect
the rotational speed of the ring gear r. In the embodiment, the input
member I is drivably coupled to the second rotary element coupling member
42 to rotate together with the second rotary element coupling member 42,
and the rotational speed of the carrier ca is equal to the rotational
speed of the internal combustion engine E at all times.

[0128] FIG. 7 is a velocity diagram illustrating operation of internal
combustion engine stop control executed by the vehicle drive device 1
according to the embodiment. In FIG. 7, as in FIG. 3, the thick solid
line represents a state of operation in the hybrid travel mode, the thin
spaced broken line (thin dotted line) represents a state in which the
rotational speed of the first rotary electric machine MG1 has reached the
connection release rotational speed Ni, and the thick broken line
represents a state of operation in the electric travel mode. In the
embodiment, the friction engagement device CL is provided to selectively
drivably couple the ring gear r to the output member O and the second
rotary electric machine MG2. Therefore, in the example, after a command
to release engagement of the friction engagement device CL is issued in
the state indicated by the thin spaced broken line (thin dotted line),
the rotational speed of the ring gear r, which has been made freely
rotatable with the friction engagement device CL brought into the
disengaged state, is reduced in accordance with a reduction in rotational
speed of the first rotary electric machine MG1 and a reduction in
rotational speed of the internal combustion engine E. In the electric
travel mode, the rotational speed of the ring gear r is basically brought
to zero.

3. Third Embodiment

[0129] Next, a vehicle drive device according to a third embodiment of the
present invention will be described with reference to FIGS. 8 and 9. As
shown in FIG. 8, the vehicle drive device 1 according to the embodiment
is basically configured in the same manner as that according to the first
embodiment described above except for the position at which the friction
engagement device CL is disposed. The differences between the
configuration of the vehicle drive device 1 according to the embodiment
and that according to the first embodiment described above will be mainly
described below. The same elements as those in the first embodiment
described above will not be specifically described.

[0130] In the vehicle drive device 1 according to the embodiment, as shown
in FIG. 8, the friction engagement device CL is provided on a power
transfer path between the first rotary electric machine MG1 and the
corresponding rotary element (first rotary element e1) of the
differential gear device DG, rather than between the input member I and
the corresponding rotary element (second rotary element e2) of the
differential gear device DG. This makes the differential gear device DG
capable of releasing the drivable connection between the first rotary
electric machine MG1 and the corresponding rotary element (first rotary
element e1) of the differential gear device DG.

[0131] Specifically, the first rotor shaft 7 of the first rotary electric
machine MG1 is drivably coupled to the first engagement member CLa, which
is one of the engagement members of the friction engagement device CL, to
rotate together with the first engagement member CLa, and the first
rotary element coupling member 41 is drivably coupled to the second
engagement member CLb, which is the other engagement member of the
friction engagement device CL, to rotate together with the second
engagement member CLb. In the embodiment, the sun gear s serves as the
rotary element to be released en. Therefore, as shown in FIG. 8, the
rotary element-to-be-released sensor Se4 is disposed so as to be able to
detect the rotational speed of the sun gear s. In the embodiment, the
input member I is drivably coupled to the second rotary element coupling
member 42 to rotate together with the second rotary element coupling
member 42, and the rotational speed of the carrier ca is equal to the
rotational speed of the internal combustion engine E at all times.

[0132] FIG. 9 is a velocity diagram illustrating operation of internal
combustion engine stop control executed by the vehicle drive device 1
according to the embodiment. In FIG. 9, as in FIG. 3, the thick solid
line represents a state of operation in the hybrid travel mode, the thin
spaced broken line (thin dotted line) represents a state in which the
rotational speed of the first rotary electric machine MG1 has reached the
connection release rotational speed Ni, and the thick broken line
represents a state of operation in the electric travel mode. The thick
broken circle which represents the first rotary electric machine MG1
represents the rotational speed of the first rotary electric machine MG1
in the electric travel mode. In the embodiment, the friction engagement
device CL is provided to selectively drivably couple the sun gear s and
the first rotary electric machine MG1 to each other. Therefore, in the
example, after a command to release engagement of the friction engagement
device CL is issued in the state indicated by the thin spaced broken line
(thin dotted line), the rotational speed of the sun gear s, which has
been made freely rotatable with the friction engagement device CL brought
into the disengaged state, is reduced in accordance with a reduction in
rotational speed of the internal combustion engine E. In the electric
travel mode, the sun gear s rotates at a rotational speed determined on
the basis of the vehicle speed (the rotational speed of the output member
O).

4. Fourth Embodiment

[0133] In the first, second, and third embodiments described above, the
first rotary electric machine MG1 is drivably coupled to the first rotary
element e1, the input member I is drivably coupled to the second rotary
element e2, and the second rotary electric machine MG2 and the output
member O are drivably coupled to the third rotary element e3, via no
other rotary element of the differential gear device DG. However, the
present invention is not limited thereto. As shown in FIG. 10, the input
member I may be drivably coupled to the first rotary element e1, the
second rotary electric machine MG2 and the output member O may be
drivably coupled to the second rotary element e2, and the first rotary
electric machine MG1 may be drivably coupled to the third rotary element
e3.

[0134] In the example shown in FIG. 10, unlike the first, second, and
third embodiments described above, a torque converter mode in which
torque obtained by amplifying output torque of the internal combustion
engine E is transferred to the output member O is basically established
in the hybrid travel mode in which the vehicle is run using output torque
of both the internal combustion engine E and the rotary electric machines
MG1 and MG2. In the embodiment, as in the first embodiment (FIG. 1)
described above, the friction engagement device CL is provided on a power
transfer path between the input member I and the corresponding rotary
element (in the example, the first rotary element e1) of the differential
gear device DG.

[0135] FIG. 10 is a velocity diagram illustrating operation of internal
combustion engine stop control executed by the vehicle drive device 1
according to the embodiment. In the drawing, λ1 and λ2
represent the gear ratio of the differential gear device DG. The values
of λ1 and λ2 are determined on the basis of the gear ratio of
a differential gear mechanism forming the differential gear device DG.
The notational system of the velocity diagram is the same as that in each
of the embodiments discussed above, and therefore is not described in
detail here. In the embodiment, unlike each of the embodiments described
above, the order of the respective rotational speeds of the reaction
force transfer element Em, the input rotary element Ei, and the output
rotary element Eo is determined such that the rotational speed of the
input rotary element Ei does not come between the respective rotational
speeds of the other two. Therefore, the subject rotational direction K2
is the same as the rotational direction of the output member O. Hence, in
the embodiment, in the case where the stop condition establishing
rotational direction K1 is the negative direction, it is determined that
the stop condition establishing rotational direction K1 is opposite to
the subject rotational direction K2.

[0136] In the embodiment, unlike each of the embodiments described above,
the order of the respective rotational speeds of the reaction force
transfer element Em, the input rotary element Ei, and the output rotary
element Eo is determined such that the rotational speed of the output
rotary element Eo comes between the respective rotational speeds of the
other two. Therefore, the direction of the rotation reducing torque is
the positive direction. In such a configuration, it is suitable that the
connection release rotational speed Ni should be set to a rotational
speed that is equal to or less than zero (zero or negative) and that is
included in the connection release rotational speed range A. In the
example of FIG. 10, the connection release rotational speed Ni is set to
a negative rotational speed included in the connection release rotational
speed range A. In the example shown in FIG. 10, the connection release
rotational speed range A is set so as to include both a rotational speed
range in which the rotational speed is positive and a rotational speed
range in which the rotational speed is negative. However, the connection
release rotational speed range A may be set so as to include only a
rotational speed range in which the rotational speed is negative in
addition to zero.

[0137] Although not shown, the configuration shown in FIG. 10 may be
modified such that the friction engagement device CL is provided on a
power transfer path between the output member O and the second rotary
electric machine MG2 and the corresponding rotary element (in the
example, the second rotary element e2) of the differential gear device
DG, or on a power transfer path between the first rotary electric machine
MG1 and the corresponding rotary element (in the example, the third
rotary element e3) of the differential gear device DG, rather than on a
power transfer path between the input member I and the rotary element of
the differential gear device DG.

5. Other Embodiments

[0138] Lastly, other embodiments of the present invention will be
described. The characteristics disclosed in each of the following
embodiments are not only applicable to that particular embodiment but
also to any other embodiment unless any contradiction occurs.

[0139] (1) In each of the embodiments described above, the second rotary
electric machine MG2 is drivably coupled to the rotary element of the
differential gear device DG to which the output member O is drivably
coupled, via no other rotary element of the differential gear device DG.
However, the present invention is not limited thereto. The second rotary
electric machine MG2 may be drivably coupled to a rotary element other
than the rotary element of the differential gear device DG to which the
output member O is drivably coupled, via no other rotary element of the
differential gear device DG.

[0140] An example of such a configuration is shown in FIG. 11, in which
the first rotary electric machine MG1 is drivably coupled to the first
rotary element e1, the input member I and the second rotary electric
machine MG2 are drivably coupled to the second rotary element e2, and the
output member O is drivably coupled to the third rotary element e3, via
no other rotary element of the differential gear device DG. In the
configuration, the friction engagement device CL is provided on a power
transfer path between the input member I and the rotary element (in the
example, the second rotary element e2) of the differential gear device DG
to which the input member I is drivably coupled via no other rotary
element, but not positioned on a power transfer path between the second
rotary electric machine MG2 and the corresponding rotary element (in the
example, the second rotary element e2) of the differential gear device
DG.

[0141] In the configuration in which the second rotary electric machine
MG2 is drivably coupled to a rotary element other than the rotary element
of the differential gear device DG to which the output member O is
drivably coupled, via no other rotary element of the differential gear
device DG as described above, unlike each of the embodiments described
above, the first rotary electric machine MG1 functions to receive a
reaction force of torque of the second rotary electric machine MG2 by
outputting torque during execution of the electric travel mode.

[0142] As an example of the configuration in which the second rotary
electric machine MG2 is drivably coupled to a rotary element other than
the rotary element of the differential gear device DG to which the output
member O is drivably coupled, via no other rotary element of the
differential gear device DG, the configuration shown in FIG. 10 may be
modified such that the second rotary electric machine MG2 is drivably
coupled to the first rotary element e1, rather than to the second rotary
element e2, although not shown. In this case, the friction engagement
device CL is provided on a power transfer path between the input member I
and the corresponding rotary element (in the example, the first rotary
element e1) of the differential gear device DG to which the input member
I is drivably coupled via no other rotary element, but not positioned on
a power transfer path between the second rotary electric machine MG2 and
the corresponding rotary element (in the example, the first rotary
element e1) of the differential gear device DG.

[0143] (2) In each of the embodiments described above, the output member O
basically rotates in the positive direction as with the internal
combustion engine E during execution of the hybrid travel mode in which
the vehicle is run utilizing output torque of the internal combustion
engine E. However, the present invention is not limited thereto. For
example, as shown in FIG. 12, the output member O may be configured to
basically rotate in the negative direction unlike the internal combustion
engine E during execution of the hybrid travel mode in which the vehicle
is run utilizing output torque of the internal combustion engine E.

[0144] In the configuration shown in FIG. 12, the input member I is
drivably coupled to the first rotary element e1, the first rotary
electric machine MG1 is drivably coupled to the second rotary element e2,
and the second rotary electric machine MG2 and the output member O are
drivably coupled to the third rotary element e3, via no other rotary
element of the differential gear device DG. In addition, the friction
engagement device CL is provided on a power transfer path between the
input member I and the rotary element (in the example, the first rotary
element e1) of the differential gear device DG to which the input member
I is drivably coupled via no other rotary element.

[0145] Although not shown, the configuration shown in FIG. 12 may be
modified such that the friction engagement device CL is provided on a
power transfer path between the first rotary electric machine MG1 and the
corresponding rotary element (in the example, the second rotary element
e2) of the differential gear device DG, or on a power transfer path
between the output member O and the second rotary electric machine MG2
and the corresponding rotary element (in the example, the third rotary
element e3) of the differential gear device DG, rather than on a power
transfer path between the input member I and the corresponding rotary
element of the differential gear device DG.

[0146] In the configuration shown in FIG. 12, the second rotary electric
machine MG2 may be drivably coupled to the first rotary element e1,
rather than to the third rotary element e3. In this case, the friction
engagement device CL is provided on a power transfer path between the
input member I and the corresponding rotary element (in the example, the
first rotary element e1) of the differential gear device DG to which the
input member I is drivably coupled via no other rotary element, but not
positioned on a power transfer path between the second rotary electric
machine MG2 and the corresponding rotary element (in the example, the
first rotary element e1) of the differential gear device DG.

[0147] (3) In each of the embodiments described above, the differential
gear device DG includes three rotary elements. However, the present
invention is not limited thereto. The differential gear device DG may
include four or more rotary elements. For example, as shown in FIGS. 13
to 15, the differential gear device DG may include four rotary elements,
namely a first rotary element e1, a second rotary element e2, a third
rotary element e3, and a fourth rotary element e4 in the order of
rotational speed. In FIGS. 13 to 15, λ1, λ2, and λ3
represent the gear ratio of the differential gear device DG. The values
of λ1, λ2, and λ3 are determined on the basis of the
gear ratio of a differential gear mechanism forming the differential gear
device DG.

[0148] In the examples shown in FIGS. 13 to 15, the input member I, the
output member O, the first rotary electric machine MG1, and the second
rotary electric machine MG2 are drivably coupled to different rotary
elements of the differential gear device DG via no other rotary element
of the differential gear device DG. That is, in the examples shown in
FIGS. 13 to 15, unlike each of the embodiments described above, the
second rotary electric machine MG2 is drivably coupled to a rotary
element other than the respective rotary elements of the differential
gear device DG to which the input member I, the output member O, and the
first rotary electric machine MG1 are drivably coupled, via no other
rotary element of the differential gear device DG.

[0149] Specifically, in the example shown in FIG. 13, the input member I
is drivably coupled to the first rotary element e1, the output member O
is drivably coupled to the second rotary element e2, the second rotary
electric machine MG2 is drivably coupled to the third rotary element e3,
and the first rotary electric machine MG1 is drivably coupled to the
fourth rotary element e4, via no other rotary element of the differential
gear device DG. In the example shown in FIG. 14, the first rotary
electric machine MG1 is drivably coupled to the first rotary element e1,
the input member I is drivably coupled to the second rotary element e2,
the output member O is drivably coupled to the third rotary element e3,
and the second rotary electric machine MG2 is drivably coupled to the
fourth rotary element e4, via no other rotary element of the differential
gear device DG. In the example shown in FIG. 15, the input member I is
drivably coupled to the first rotary element e1, the first rotary
electric machine MG1 is drivably coupled to the second rotary element e2,
the second rotary electric machine MG2 is drivably coupled to the third
rotary element e3, and the output member O is drivably coupled to the
fourth rotary element e4, via no other rotary element of the differential
gear device DG.

[0150] In the examples shown in FIGS. 13 to 15, the friction engagement
device CL is provided on a power transfer path between the input member I
and the corresponding rotary element of the differential gear device DG
to which the input member I is drivably coupled via no other rotary
element.

[0151] The configuration in which the differential gear device DG includes
four rotary elements is not limited to the examples shown in FIGS. 13 to
15, and two of the rotary elements may be reversed in order in the
configurations shown in FIGS. 13 to 15. For example, in the configuration
shown in FIG. 13, the second rotary element e2 and the third rotary
element e3 may be reversed in order. In the configuration shown in FIG.
14, in addition, the third rotary element e3 and the fourth rotary
element e4 may be reversed in order. In the configuration shown in FIG.
14, further, the third rotary element e3 and the fourth rotary element e4
may be reversed in order, and thereafter the second rotary element e2 and
the third rotary element e3 may be reversed in order.

[0152] (4) In each of the embodiments described above, the rotational
speed of the first rotary electric machine MG1 at which the rotation
reducing torque control is stopped is equal to the rotational speed of
the first rotary electric machine MG1 at which the connection release
command section 83 issues a command to release engagement of the friction
engagement device CL. However, the present invention is not limited
thereto. The rotational speed of the first rotary electric machine MG1 at
which the rotation reducing torque control is stopped may be different
from the rotational speed of the first rotary electric machine MG1 at
which the connection release command section 83 issues a command to
release engagement of the friction engagement device CL. That is, the
rotation reducing torque control may be stopped before or after the
connection release command section 83 issues a command to release
engagement of the friction engagement device CL. In this ease, the
rotational speed of the first rotary electric machine MG1 at which the
rotation reducing torque control is stopped may be set to a rotational
speed not included in the connection release rotational speed range A.

[0153] (5) In each of the embodiments described above, rotation reducing
torque control is stopped before the rotational direction of the first
rotary electric machine MG1 becomes the same as the subject rotational
direction K2. However, the present invention is not limited thereto. The
rotation reducing torque control may be stopped after the rotational
direction of the first rotary electric machine MG1 becomes the same as
the subject rotational direction K2.

[0154] (6) In each of the embodiments described above, the engagement
release command issued by the connection release command section 83 is
executed before the rotational direction of the first rotary electric
machine MG1 becomes the same as the subject rotational direction K2.
However, the present invention is not limited thereto. The connection
release rotational speed range A may be set so as to include a rotational
speed range in which the rotational direction of the first rotary
electric machine MG1 is the same as the subject rotational direction K2,
and the engagement release command issued by the connection release
command section 83 may be executed after the rotational direction of the
first rotary electric machine MG1 becomes the same as the subject
rotational direction K2.

[0155] (7) In each of the embodiments described above, the fluctuation
suppressing control is executed at least during a period since the
internal combustion engine stop conditions are established until the
drivable connection made by the friction engagement device CL is
released. However, the present invention is not limited thereto. The
fluctuation suppression control may be not executed during a part or all
of the period since the internal combustion engine stop conditions are
established until the drivable connection made by the friction engagement
device CL is released. Alternatively, in the case where the friction
engagement device CL is in the engaged state (the slip engagement state
or the directly engaged state) while the vehicle is traveling, the
fluctuation suppressing control may be basically executed at all times.

[0156] (8) In the first, second, and third embodiments described above,
the differential gear device DG is formed by the planetary gear mechanism
PG of a single pinion type. However, the present invention is not limited
thereto. The differential gear device DG may be formed by a planetary
gear mechanism of a double pinion type or a planetary gear mechanism of a
Ravigneaux type. Also in each of the embodiments in which the specific
configuration of the differential gear device DG is not indicated
(embodiments excluding the first, second, and third embodiments described
above), the differential gear device DG may be formed by any mechanism.
For example, the differential gear device DG including four or more
rotary elements may be formed by two or more planetary gear mechanisms,
some rotary elements of which are coupled to each other.

[0157] (9) In each of the embodiments described above, the friction
engagement device CL is a friction engagement device that operates on a
hydraulic pressure. However, the present invention is not limited
thereto. The friction engagement device CL may be an electromagnetic
friction engagement device, the engagement pressure of which is
controlled in accordance with an electromagnetic force. In each of the
embodiments described above, in addition, the engagement device according
to the present invention is implemented by the friction engagement device
CL. However, the engagement device according to the present invention may
be implemented by a meshing-type engagement device (dog clutch).

[0158] (10) In each of the embodiments described above, the internal
combustion engine control unit 3, the friction engagement device control
unit 6, and the brake device control unit 8 are provided separately from
the control device 70. However, the present invention is not limited
thereto. At least one of the control units may be integrated in the
control device 70. The configuration of the functional sections described
in relation to the embodiments described above is merely illustrative,
and a plurality of functional sections may be combined with each other,
or a single functional section may be further divided into sub-sections.

[0159] (11) Also regarding other configurations, the embodiments disclosed
herein are illustrative in all respects, and the present invention is not
limited thereto. That is, it is a matter of course that a configuration
obtained by appropriately altering part of a configuration not disclosed
in the claims of the present invention also falls within the technical
scope of the present invention as long as the resulting configuration
includes a configuration disclosed in the claims or a configuration
equivalent thereto.

[0160] The present invention may be suitably applied to a vehicle drive
device including an input member drivably coupled to an internal
combustion engine, an output member drivably coupled to wheels, a first
rotary electric machine, a second rotary electric machine, a differential
gear device including at least three rotary elements, and a control
device.